sched, preempt_notifier: separate notifier registration from static_key inc/dec
Commit 1cde2930 ("sched/preempt: Add static_key() to preempt_notifiers") had two problems. First, the preempt-notifier API needs to sleep with the addition of the static_key, we do however need to hold off preemption while modifying the preempt notifier list, otherwise a preemption could observe an inconsistent list state. KVM correctly registers and unregisters preempt notifiers with preemption disabled, so the sleep caused dmesg splats. Second, KVM registers and unregisters preemption notifiers very often (in vcpu_load/vcpu_put). With a single uniprocessor guest the static key would move between 0 and 1 continuously, hitting the slow path on every userspace exit. To fix this, wrap the static_key inc/dec in a new API, and call it from KVM. Fixes: 1cde2930 ("sched/preempt: Add static_key() to preempt_notifiers") Reported-by: NPontus Fuchs <pontus.fuchs@gmail.com> Reported-by: NTakashi Iwai <tiwai@suse.de> Tested-by: NTakashi Iwai <tiwai@suse.de> Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Showing
想要评论请 注册 或 登录